Method of making an output filter for an image intensifier tube with color reproduction and an output made according to this method

ABSTRACT

The invention provides a method of making an output filter for an image intensifier tube for colour display, which output filter is a reproduction of the image intensifier tube in order to avoid the influence of the distortion introduced by the tube.

United States Patent [1 1 [111 3,801,739 Geluk Apr. 2, 1974 154] METHOD OF-MAKING AN OUTPUT FILTER FOR AN IMAGE INTENSIFIER TUBE WITH COLOR REPRODUCTION AND AN OUTPUT MADE ACCORDING TO THIS METHOD Ronald Jan Geluk, Nootdorp, Netherlands N.V. Optische Industrie De Oude Deift, Delft, Netherlands Filed: Mar. 13, 1972 Appl. No.: 234,183

Inventor:

Assignce:

Foreign Application Priority Data Mar. 25, 1971 Netherlands 7103991 US. Cl. l78/7.85 Int. Cl. H0lj 31/20 Field of Search 178/7.85, 5.4 ST; 316/1,

[56] References Cited UNITED STATES PATENTS 3,124,784 3/1964 Schaaf et a1. 340/1725 3,647,943 3/1972 Marshall 1 178/54 ST 3,586,434 6/1971 Mueller 178/54 ST 3,164,744 1/1965 Bowkcr 178/7.85 3,637,925 1/1972 Flory et a1 178/5.4 ST 3,582,984 6/1971 Kurokawa 178/5.4 ST

Primary Examiner-Gareth D. Shaw Attorney, Agent, or FirmArthur B. Colvin 57 ABSTRACT The invention provides a method of making an output filter for an image intensifier tube for colour display, which output filter is a reproduction of the image intensifier tube in order to avoid the influence of the distortion introduced by the tube.

5 Claims, 4 Drawing Figures 1 METHOD OF MAKING AN OUTPUT FILTER FOR AN IMAGE INTENSIFIER TUBE WITH COLOR REPRODUCTION AND AN OUTPUT MADE ACCORDING TO THIS METHOD The invention relates to a method of making an output filter by means of which the image on the anode screen of an image intensifier tube containing white phosphorus and having an input and output fibre whose photo cathode receives an image via an input filter, can be transformed into a color image, wherein the input filter contains groups of regions each of which groups can transmit different parts of the spectrum, and an output filter made according to this method.

It is known, for example, to mount a raster film with red, green and blue strips against the input fibre of an image intensifier tube and afterwards to transfer the image on the anode screen on to a black-and-white film and then to view the image on the black-and-white film via a raster filter that is identical to the first filter. This shows the drawback that the distortion of the image introduced by the image intensifier tube, and hence also the distortion of the image of the input filter, has the result that the lines of the image on the anode screen do not cover the lines in this latter raster filter.

The object of the invention is to provide a method of making an output filter not showing this drawback. The method according to the invention is to this end characterized in that the output filter is made in the form of a reproduction of the image of the input filter on the anode screen of the image intensifier tube.

The invention is further elucidated by reference to the drawing for the special case in which the filter contains red, green and blue strips.

FIG. 1 shows in outline an image intensifier tube with input and output filters.

FIG. 2 shows a black-and-white raster with the aid of which an input color raster has been made.

FIG. 3 shows in outline a set-up in which the blackand-white raster is placed against the input of the image intensifier tube in order to make a black-and-white raster that corresponds to the image formed on the anode screen of the image intensifier tube.

FIG. 4 shows in outline the method of making a color raster from the black-and-white raster made last.

In FIG. 1 an image intensifier tube 1 is shown with an input raster filter 2 and an output raster filter 3, each containing groups of red (R), green (G) and blue (B) strips. An image falling via the input raster filter 2 upon the photo cathode of the image intensifier tube 1 is formed on the anode screen containing white phosphorus and will be observed as a colored image via the output raster filter 3.

FIG. 2 shows an input raster filter 2and a black-andwhite raster 4 with dark strips 5, which hs been used for making the input raster filter 2 FIG. 3 shows the condition in which the black-andwhite raster 4 is mounted at the position of the input raster filter 2-in such a way that strips 5 occupy the position of the strips R in filter 2. The photo cathode of the image intensifier tube 1 isnow exposed via the raster filter 4, and the anode screen isimaged l l on the blackand-white film 6. 7

After this, as shown in FIG. 4, the black-and-white raster is imaged on a film 7 which, after development in the exposed parts, only transmits, for instance, red, green or blue, and furthermore the entire spectrum, A suitable film for this is, for instance, 3M Colorkey.

These operations are repeated for the green and blue strips. The three prints are then combined on film portions 7 and are mounted precisely behind the anode screen of the image intensifier tube. It is to be noted that in many cases it will be sufficientto use one blackand-white raster 6 for making the three prints on film portions 7.

It will be obvious that the invention is not restricted to the use of raster filters and that other colors than red, green and blue or overlapping parts of the spectrum may also be used.

What I claim is:

l. The method of making an improved distortion compensated output filter for viewing the image on the anode screen of an image intensifier tube of the type including a cathode, an anode having a white phosphor screen and an input filter through which light is impinged on the cathode, the filter being dividedinto regularly spaced groups of regions, the regions of each group being adapted to transmit different clors of the spectrum than the colors transmitted bythe regions of the other groups, comprising the steps. of forming on said anode screen an image of one of said groups of regions only and photographically producing a replica of said formed image depicting the regions of said one group in the color in which they appear in the input filter, repeating said steps for each said color, and superimposing the thus formed replicas, said superimposed replicas thus constituting a reproduction of said input filter modified by the distortions produced within said tube.

2. The method of making an image intensifier tube including an improved distortion compensated output filter for viewing the image on the anode screen, said image intensifier tube being of the type including a cathode, an anode having a white phosphor screen and an input filter through which light is impinged on the cathode, the filter being divided into regularly spaced groups of regions, the regions of each group being adapted to transmit different colors of the spectrum than the colors transmitted by the regions of the other groups, comprising the steps of providing a mask having a pattern of light passing and light impervious portions corresponding to the regions of a single one of said groups, positioning said mask between said cathode and a light source, thereby exposing said cathode to light passed through said mask, thus to cause the formation on said anode screen of a pattern corresponding to the pattern of said one group modified by the distortions inhering in said tube, thereafter producing a replica. of said formed image on said anode screen depicting the regions of said one group in the color in which they appear on said input filter, and thereafter mounting said replica over said anode screen with the regions of said replica in registry with the regions of said image on said screen.

3. An image intensifier tube incorporating an improved distortion compensated output filter apparatus for viewing the image on the anode screen, said tube being of the type including a cathode, an anode having a white phosphor screen and an input filter through which light is impinge on the cathode, the filter being divided into equally spaced groups of regions, the regions of each group being adapted to transmit different colors of the spectrum than the colors transmitted by the regions of the other groups made in accordance with the method ofclaim 2.

4. The method of claim 2 wherein said replica of said producing a replica of said formed image are repeated image on said anode screen is photographically reproduced on a 1 1 ratio.

5. The method of claim 2 wherein the steps of posiposed to provlde a fimshped filtertioning a mask, forming an image on said screen, and 5 for each group, the replicas thus formed being superim- 

1. The method of making an improved distortion compensated output filter for viewing the image on the anode screen of an image intensifier tube of the type including a cathode, an anode having a white phosphor screen and an input filter through which light is impinged on the cathode, the filter being divided into regularly spaced groups of regions, the regions of each group being adapted to transmit different clors of the spectrum than the colors transmitted by the regions of the other groups, comprising the steps of forming on said anode screen an image of one of said groups of regions only and photographically producing a replica of said formed image depicting the regions of said one group in the color in which they appear in the input filter, repeating said steps for each said color, and superimposing the thus formed replicas, said superimposed replicas thus constituting a reproduction of said input filter modified by the distortions produced within said tube.
 2. The method of making an image intensifier tube including an improved distortion compensated output filter for viewing the image on the anode screen, said image intensifier tube being of the type including a cathode, an anode having a white phosphor screen and an input filter through which light is impinged on the cathode, the filter being divided into regularly spaced groups of regions, the regions of each group being adapted to transmit different colors of the spectrum than the colors transmitted by the regions of the other groups, comprising the steps of providing a mask having a pattern of light passing and light impervious portions corresponding to the regions of a single one of said groups, positioning said mask between said cathode and a light source, thereby exposing said cathode to light passed through said mask, thus to cause the formation on said anode screen of a pattern corresponding to the pattern of said one group modified by the distortions inhering in said tube, thereafter producing a replica of said formed image on said anode screen depicting the regions of said one group in the color in which they appear on said input filter, and thereafter mounting said replica over said anode screen with the regions of said replica in registry with the regions of said image on said screen.
 3. An image intensifier tube incorporating an improved distortion compensated output filter apparatus for viewing the image on the anode screen, said tube being of the type including a cathode, an anode having a white phosphor screen and an input filter through which light is impinge on the cathode, the filter being divided into equally spaced groups of regions, the regions of each group being adapted to transmit different colors of the spectrum than the colors transmitted by the regions of the other groups made in accordance with the method of claim
 2. 4. The method of claim 2 wherein said replica of said image on said anode screen is photographically reproduced on a 1 : 1 ratio.
 5. The method of claim 2 wherein the steps of positioning a mask, forming an image on said screen, and producing a replica of said formed image Are repeated for each group, the replicas thus formed being superimposed to provide a finished filter. 